Nitrates and Nitrites in Drinking Water

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Nitrate Fact Sheet

What is nitrate?

Nitrates can be found in drinking water supplies. Their presence in groundwater is generally associated with septic systems, confined animal feeding operations, or fertilizer use. These sources of nitrate contamination are more associated with rural settings, and are often subjects of drinking water source protection programs.

Nitrates are also present in treated wastewater, and as such can be present in surface water, or in treated wastewater used in groundwater recharge projects. These sources can pose risks to urban drinking water supplies.

Nitrates are also used in industry, for example, in the production of fertilizers and explosives.

What's the concern about nitrate/nitrite in drinking water?

Nitrite can interfere with the ability of red blood cells to carry oxygen to the tissues of the body, producing a condition called methemoglobinemia. It is of greatest concern in infants, whose immature stomach environment enables conversion of nitrate to nitrite, which is then absorbed into the blood stream. The effects of nitrite are often referred to as the "blue baby syndrome. High nitrate levels may also affect the oxygen-carrying ability of the blood of pregnant women. These potential effects are identified in notification requirements [22 CCR §64465, Appendix 64465.D]

The Office of Environmental Health Hazard Assessment (OEHHA) established its public health goals (PHGs) for nitrate and nitrite (PDF) in 1997. The PHGs, based on methemoglobinemia in the infant, are the same as the MCLs.

There's more information on nitrates and nitrites from the websites listed below.

What are the MCLs for nitrate in drinking water?

The MCLs, in 22 CCR §63341, 10 mg/L for nitrate as nitrogen (N); 10 mg/L for nitrate plus nitrite as N; and 1 mg/L for nitrite as N.

Where's nitrate been found in drinking water in California?

Public water systems, because they are regulated by the State, (unlike private wells) , are required to analyze for nitrates and report the results to DDW. Among regulated contaminants detected at levels greater than their MCLs in California, nitrates rank high. For example, based on monitoring data submitted to the Department of Public Health’s Drinking Water Program, DDW’s precursor, from 2002-2005, there were these findings:

  • Nitrate as NO3 (the prior nitrate standard, now nitrate as N) was detected at least once above its MCL in 731 sources. The counties with the greatest number of sources include Los Angeles (123 sources), San Bernardino (82), Riverside (67), Kern (41), and Monterey (30)
  • Nitrate + nitrite as N was detected at least once above its MCL in 169 sources. Sources per county include San Bernardino (38), Los Angeles (36), and Riverside (24)
  • Nitrite as N was detected at least once above its MCL in 21 sources. The counties with the greatest number of sources include: Alameda (7), San Joaquin (5), and Kern (4)

More recent data from DDW along with maps are included in the GAMA Program's fact sheet for nitrate (PDF).

What about water from private wells?

  • Private wells are not subject to drinking water regulation by DDW. They are not public water systems - see 22 CCR §116275 (h).
  • The MCLs can be used for guidance.

Where can I find laboratories that can do nitrate analyses?

The Environmental Laboratory Accreditation Program (ELAP) certifies analytical laboratories, and lists certified laboratories on its website.

What other information is available?

There's more from these sites:

More Information for Water Systems

Division of Drinking Water


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State Water Resources Control Board
Division of Drinking Water
Regulatory Development Unit

Mailing Address:
P.O. Box 100
Sacramento, CA 95812-0100

Street Address:
1001 I Street
Sacramento, CA 95814

E-mail us at DDWRegUnit@waterboards.ca.gov.